The present invention relates to a radar rangefinder as claimed in the descriptive part of patent claim 1.
Such a radar rangefinder is used, for example, in an arrangement for monitoring a danger area, as is illustrated and described in DE 196 12 579 A1 from the same applicant.
In the FMCW radar (frequency-modulated continuous-wave radar) used there, temperature-dependent and age-dependent changes normally prevent a desired strictly linear frequency/time function. The voltage-controlled oscillators in the available transmitters have non-linear drive characteristics which are highly dependent on temperature, load and the operating voltage.
In this context, it is known for calibration methods to be used, which use a target which produces an echo at a known distance. This allows self-calibration to be carried out, using the Hilbert transformation. However, the arrangement of a target which produces an echo at a known distance has various disadvantages. Firstly, this target can be concealed by people or objects moving in the area. Secondly, raindrops, snow or ice in the measurement path or on the radome housing in which the radar rangefinder is arranged can adversely affect the calibration. On the other hand, it is desirable for the calibration distance to be as great as possible in order to keep the calibration measurement error as small as possible.
Against this background, the object of the present invention is to specify a radar rangefinder having a reflector for calibration, in which the disturbance influences mentioned above are all precluded.
This object is achieved according to the distinguishing features of patent claim 1. Further advantageous refinements of the radar rangefinder according to the invention can be found in the dependent claims.
The invention will be described in more detail in the following text with reference to an exemplary embodiment which is illustrated in the figures of the attached drawing, in which: